Triggering terminal roaming by access point

ABSTRACT

This application relates to the communications field, and in particular, to a method for triggering terminal roaming by an access point (AP) and an access point. In the method, a first AP sends, by using a first channel, a unicast channel switching message to a first terminal associated with the first AP, where the unicast channel switching message is used to instruct the first terminal to switch from the first channel to a second channel, a receiver address of the unicast channel switching message is an address of the first terminal, the first channel is an operating channel of the first AP, and the second channel and the first channel are different; and retains the first channel as the operating channel of the first AP after the unicast channel switching message is sent. According to the method, a process of associating with a new AP can be simplified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201610257449.5, filed on Apr. 22, 2016, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

Embodiments of this disclosure relate to the communications field, andin particular, to a method for triggering terminal roaming by an accesspoint (AP) and an access point.

BACKGROUND

In a wireless local area network (WLAN), if an access point needs totrigger terminal roaming, for a terminal that supports wireless networkmanagement, an AP associated with the terminal can instruct, by using abasic service set transition mechanism, the terminal to roam and toassociate with a new AP. For a terminal that does not support wirelessnetwork management, an AP currently associated with the terminal sends adisassociation frame or a deauthentication frame to the terminal, so asto disassociate from the terminal and trigger terminal roaming.

However, after disassociating from the original AP, the terminal thatdoes not support wireless network management becomes a terminal that isnot associated with any AP. When the terminal that is not associatedwith any AP attempts to associate with a new AP, the terminal may needto be re-authenticated, resulting in a long service interruption time ofthe terminal.

SUMMARY

This application describes a method for triggering terminal roaming byan access point and an access point, so that an AP can trigger smoothroaming of a terminal.

According to a first aspect, a method for triggering terminal roaming byan access point is provided. The method includes: sending, by a first APby using a first channel, a unicast channel switching message (forexample, a unicast channel switch announcement (CSA) frame) to a firstterminal associated with the first AP, where the unicast channelswitching message is used to instruct the first terminal to switch fromthe first channel to a second channel, a receiver address (RA) of theunicast channel switching message is an address of the first terminal,the first channel is an operating channel of the first AP, and thesecond channel and the first channel are different; and retaining thefirst channel as the operating channel of the first AP after the unicastchannel switching message is sent.

The first AP instructs a terminal associated with the first AP to switchto another channel, but the first AP remains on the original operatingchannel. The first AP does not use a new operating channel for working.After switching to a new operating channel, the terminal cannot find theAP associated with the terminal, and attempts to associate with a newAP. Because the terminal is in an associated state at this moment, aprocess of associating with a new AP can be simplified. In this way, theAP triggers smooth roaming of the terminal.

In optional implementation, the first AP receives an instruction messagesent by a second AP. The instruction message instructs a second terminalassociated with the second AP to switch to the first channel, and theinstruction message includes a basic service set identifier (BSSID) ofthe second AP and an address of the second terminal. The BSSID may be aradio medium access control (MAC) address of the second AP. An operatingchannel of the second AP and the first channel are different. The firstAP transmits a data frame to the second terminal according to theaddress of the second terminal. The address may be a MAC address of thesecond terminal. A BSSID field of the data frame is filled in with theBSSID of the second AP.

After the second terminal hands over to the first AP on the firstoperating channel, the first AP sends and receives a data frame for thesecond terminal by simulating the second AP according to the MAC addressof the second terminal and the BSSID of the second AP, so that thesecond terminal can still send and receive a data frame normally. Thatis, before the second terminal roams, a service interruption time of thesecond terminal is reduced.

In optional implementation, the first AP receives an instruction messagesent by a second AP. The instruction message instructs a second terminalassociated with the second AP to switch to the first channel, and theinstruction message includes a BSSID of the second AP and an address ofthe second terminal. An operating channel of the second AP and the firstchannel are different. The first AP sends a simulation beacon frame tothe second terminal at a first power by using the first channel. A firstaddress field of the simulation beacon frame includes the address of thesecond terminal, a second address field of the simulation beacon frameincludes the BSSID of the second AP, and a third address field of thesimulation beacon frame includes the BSSID of the second AP. The firstpower is less than a default transmit power of the first AP.

After the second terminal switches to the operating channel of the firstAP, the first AP can send, at a power that is less than the defaulttransmit power of the first AP, the simulation beacon frame to thesecond terminal by means of unicast, or send, at a gradually decreasingtransmit power, the simulation beacon frame to the second terminal bymeans of unicast. When a simulation beacon frame signal detected by thesecond terminal is weak, it is very likely that the second terminalproactively initiates roaming. Therefore, in this implementation,terminal roaming can be triggered. In addition, in another optionalmanner of triggering terminal roaming, the first AP does not send asimulation beacon frame after the second terminal switches to theoperating channel of the first AP.

In optional implementation, the first AP receives an instruction messagesent by a second AP. The instruction message includes a BSSID of thesecond AP. The instruction message instructs the first AP to send asimulation beacon frame by using the BSSID of the second AP. Anoperating channel of the second AP and the first channel are different.The first AP sends the simulation beacon frame at a first power by usingthe first channel. A first address field of the simulation beacon frameincludes a broadcast address. The first power is less than a defaulttransmit power of the first AP.

In this implementation manner, compatibility between the second terminaland the first AP is improved. In addition, in another optional manner oftriggering terminal roaming, the first AP does not send a simulationbeacon frame after the second terminal switches to the operating channelof the first AP.

In optional implementation, the first AP periodically sends multiplesimulation beacon frames to the second terminal by using the firstchannel. The multiple simulation beacon frames include the simulationbeacon frame sent at the first power. After a quantity of times that thefirst AP sends the simulation beacon frames reaches a threshold, thefirst AP stops sending the simulation beacon frames.

The first AP may periodically send, at a power that is less than adefault transmit power of the first AP, the simulation beacon frames tothe second terminal by means of unicast/broadcast, or periodically send,at a gradually decreasing transmit power, the simulation beacon framesto the second terminal by means of unicast/broadcast, and stop sendingthe simulation beacon frames to the second terminal when the quantity oftimes of sending the simulation beacon frames reaches the threshold (forexample, three or four simulation beacon frames).

According to a second aspect, an access point is provided. The accesspoint has functions of implementing actual access point behavior in theforegoing method. The functions may be implemented by using hardware orby executing corresponding software by hardware. The hardware orsoftware includes one or more modules corresponding to the functions.

According to a third aspect, an access point is provided. The accesspoint includes a transceiver and a processing circuit. The processingcircuit sends, by using the transceiver and a first channel, a unicastchannel switching message to a first terminal associated with the AP.The unicast channel switching message is used to instruct the firstterminal to switch from the first channel to a second channel. Areceiver address of the unicast channel switching message is an addressof the first terminal. The first channel is an operating channel of theAP. The second channel and the first channel are different. After theunicast channel switching message is sent, the processing circuitretains the first channel as the operating channel of the AP.

The access point may further include a memory. The memory is configuredto couple with the processing circuit and store a program instructionand data that are necessary for the access point.

According to another aspect, a computer storage medium is provided. Thecomputer storage medium is configured to store a computer softwareinstruction used for the foregoing access point, and the computersoftware instruction includes a program that is designed for executingthe foregoing aspects.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly describes the accompanyingdrawings required for describing the embodiments. Apparently, theaccompanying drawings in the following description show only someembodiments of the present invention, and a person of ordinary skill inthe art may still derive other drawings from these accompanying drawingswithout creative efforts.

FIG. 1 is a schematic structural diagram of a WLAN system according tothe present invention;

FIG. 2 is an information interaction diagram of a method for triggeringterminal roaming by an access point according to an embodiment of thepresent invention;

FIG. 3 is a schematic structural diagram of an access point according toan embodiment of the present invention; and

FIG. 4 is a schematic structural diagram of another access pointaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The technical solutions of the present invention are further describedin detail with reference to accompanying drawings and embodiments asfollows:

A method for triggering terminal roaming by an access point provided inthis application is applied to a WLAN system, and the WLAN system mayinclude a terminal and at least two APs. Optionally, the WLAN system mayfurther include a controller. For example, if a Control And Provisioningof Wireless Access Points (CAPWAP) protocol runs between an AP and thecontroller, the controller is an access controller (AC) in the CAPWAPprotocol, and the AP is a wireless termination point (WTP) in the CAPWAPprotocol.

A WLAN system shown in FIG. 1 is used as an example for description. TheWLAN system includes a terminal and two APs. The two APs are an AP 1 andan AP 2. In the following descriptions, an AP that is associated withthe terminal before channel switching is referred to as a first AP, andan AP that is associated with the terminal after channel switching isreferred to as a second AP. In a process described below in thisspecification, the AP 1 is the first AP, and the AP 2 is the second AP.

The terminal in FIG. 1 may be, for example, a mobile phone, a tabletcomputer, a personal computer, or a wearable device. The terminal doesnot support wireless network management. Optionally, the WLAN system mayfurther include a terminal that supports wireless network management.For a terminal that supports wireless network management, an APassociated with the terminal can instruct, by using a mechanism definedin a wireless network management protocol, the terminal to roam to an APwith which the terminal finally needs to associate, that is, a targetAP. Before the terminal associates with the first AP, the terminal needsto send an association request frame to the first AP. The associationrequest frame may include a capability of the terminal, so that thefirst AP can determine whether the terminal supports the wirelessnetwork management protocol.

FIG. 2 is an information interaction diagram of a method for triggeringterminal roaming by an access point according to an embodiment of thepresent invention. As shown in FIG. 2, the method may include thefollowing step:

Step 210: A first AP sends, by using a first channel, a unicast channelswitching message to a first terminal associated with the first AP,where the unicast channel switching message is used to instruct thefirst terminal to switch from the first channel to a second channel, areceiver address (RA) of the unicast channel switching message is anaddress of the first terminal, the first channel is an operating channelof the first AP, and the second channel and the first channel aredifferent; and retains the first channel as the operating channel of thefirst AP after the unicast channel switching message is sent.

Herein, the unicast channel switching message may be a unicast channelswitch announcement (CSA) frame. The unicast CSA frame includesinformation about the second channel, and a receiver address of the CSAframe is a medium access control (MAC) address of the first terminal.The MAC address of the first terminal is a unicast address.

Optionally, before the first AP sends the unicast channel switchingmessage to the first terminal associated with the first AP, the first APcan identify, according to a preset first algorithm, whether the firstterminal meets a roaming condition. The first AP sends the unicastchannel switching message to the first terminal if the first terminalmeets the roaming condition, so as to trigger roaming of the firstterminal. Alternatively, the first AP may receive an instruction fromthe controller, and determine that the first terminal meets the roamingcondition and trigger roaming of the first terminal.

The first AP sends, by using the first channel, the unicast channelswitching message to the first terminal associated with the first AP.Generally, a conventional channel switching message instructs the firstAP and the first terminal associated with the first AP to simultaneouslyswitch to the second channel. However, the unicast channel switchingmessage is sent by the first AP to delude the first terminal intoperforming a channel switching operation. That is, the unicast channelswitching message instructs the first terminal to switch to the secondchannel (that is, instructs the first terminal to leave the firstchannel), but the first AP does not switch to the second channel andremains on the current first channel.

The second channel may be any channel that is different from the firstchannel. Optionally, the second channel may be an operating channel ofanother AP.

After switching to the second channel, the first terminal cannot findthe first AP, and attempts to associate with a new AP. Because the firstterminal is in an associated state at this moment, a process ofassociating with a new AP can be simplified. It can be learnt that theunicast channel switching message makes a process of switching performedby the first terminal relatively smooth.

Optionally, after sending the unicast channel switching message to thefirst terminal, the first AP can send an empty data frame to detectwhether the first terminal has left the first operating channel of thefirst AP. If the first AP receives a response frame returned by thefirst terminal, the first terminal has not left the first operatingchannel of the first AP, that is, the first terminal still stays on thefirst operating channel of the first AP. If the first AP does notreceive a response message returned by the first terminal, the firstterminal may have left the first operating channel of the first AP.

When the first AP detects that the first terminal has not left the firstchannel, the first AP can send a unicast channel switching message tothe first terminal again. If the first terminal still stays on the firstAP, the first AP can send a disassociation message to the firstterminal, to disassociate the first AP from the first terminal. Thedisassociation message may be a disassociation frame or adeauthentication frame. Alternatively, the first AP may send adisassociation message after sending more unicast channel switchingmessages to the first terminal.

Optionally, if the second channel is an operating channel of the secondAP, the first AP can send an instruction message to the second AP. Theinstruction message instructs the first terminal associated with thefirst AP to switch to the second channel. The instruction messageincludes a basic service set identifier (BSSID) of the first AP and theaddress of the first terminal. The BSSID may be a radio MAC address ofthe first AP. If the first AP has multiple BSSIDs, the BSSID in theinstruction message is a BSSID in a basic service set (BSS) associatedwith the first terminal. The second AP transmits a data frame to thefirst terminal according to the address of the first terminal. A BSSIDfield of the data frame is filled in with the BSSID of the first AP.

After the first terminal switches to the second channel according to theunicast channel switching message, where the second channel is theoperating channel of the second AP, the first AP sends an indicationmessage to the second AP to indicate that the first terminal hasswitched to the second channel that is different from the first channel.The second AP transmits, according to the address of the first terminal,the data frame that includes the BSSID of the first AP to the firstterminal, and the address may be the MAC address of the first terminal.Herein, transmission includes but is not limited to the followingbehaviors: both receiving and sending, only receiving and not sending,and only sending and not receiving.

In a process of sending a data frame from the second AP to the firstterminal, an address 1 field (that is, a receiver address) of the dataframe is filled in with the address of the first terminal, and anaddress 2 field (that is, a transmitter address (TA)) of the data frameis filled in with the BSSID of the first AP.

In a process of sending a data frame from the first terminal to thesecond AP, an address 1 field (that is, a receiver address) of the dataframe is filled in with the BSSID of the first AP, and an address 2field (that is, a transmitter address TA) of the data frame is filled inwith the address of the first terminal.

If the data frame carries an aggregate MAC service data unit (A-MSDU),an address 3 field is also filled in with the BSSID of the first AP.

The second AP transmits the data frame to the first terminal accordingto a location of the address, in the data frame, of the first terminal.The BSSID field of the data frame is a field that is in the data frameand that is filled in with a BSSID. For example, when the second APsends a data frame to the first terminal, an address 2 field of the dataframe should be filled in with a BSSID; in this case, the address 2field is a BSSID field. When the data frame carries an A-MSDU, anaddress 3 field is also a BSSID field.

After the first terminal hands over to the second AP on the secondoperating channel, the second AP sends and receives a data frame for thefirst terminal by simulating the first AP according to the MAC addressof the first terminal and the BSSID of the first AP, so that the firstterminal can still send and receive a data frame normally. That is,before the first terminal roams, a service interruption time of thefirst terminal is reduced.

Optionally, after the second AP receives the indication message sent bythe first AP, the second AP on the second channel can send, at a firstpower, a simulation beacon frame to the first terminal by means ofunicast, or send, at a first power, a simulation beacon frame to thefirst terminal by means of broadcast. The first power is less than adefault transmit power of the second AP.

A beacon frame is a management frame. A simulation beacon frame is abeacon frame sent by an AP by simulating another AP by using a BSSID ofthe another AP.

A beacon frame is generally a broadcast frame, that is, a receiveraddress of the beacon frame is generally a broadcast address. However, areceiver address of the simulation beacon frame may be the address ofthe first terminal, that is, may be a unicast address. For example, ifthe second AP sends the simulation beacon frame to the first terminal bymeans of unicast, an address 1 field (that is, a receiver address) ofthe simulation beacon frame is filled in with the address of the firstterminal, where the address may be the MAC address of the firstterminal; an address 2 field (that is, a transmitter address) of thesimulation beacon frame is filled in with the BSSID of the first AP; anaddress 3 field of the simulation beacon frame is filled in with theBSSID of the first AP. In this way, the second AP sends the simulationbeacon frame to the first terminal by simulating the first AP.

If the second AP sends the simulation beacon frame to the first terminalby means of broadcast, an address 1 field of the simulation beacon frameis filled in with a broadcast address, an address 2 field of thesimulation beacon frame is filled in with the BSSID of the first AP, andan address 3 field of the simulation beacon frame is filled in with theBSSID of the first AP. In this way, the second AP sends the simulationbeacon frame to the first terminal by simulating the first AP. When thesecond AP sends the simulation beacon frame to the first terminal bymeans of broadcast, because another terminal associated with the secondAP receives only a beacon frame whose address 2 field in the simulationbeacon frame is filled in with a BSSID of the second AP, the simulationbeacon frame that is sent to the first terminal by the second AP bysimulating the BSSID of the first AP has no effect on the anotherterminal associated with the second AP.

The first power is less than the default transmit power of the secondAP. The default transmit power is a general transmit power or a normaltransmit power at which, in a normal condition, a beacon frame is sentto a terminal associated with the second AP.

Further, the second AP can periodically send multiple simulation beaconframes to the first terminal by using the second channel. A transmitpower at which at least one of the multiple simulation beacon frames issent is the first power. For example, the second AP periodically sends,at the first power, the multiple simulation beacon frames to the firstterminal by using the second channel. Alternatively, the second APperiodically sends the multiple simulation beacon frames to the firstterminal by using the second channel, and gradually decreases a transmitpower.

The second AP can send the simulation beacon frames to the firstterminal at a power that is less than the default transmit power of thesecond AP, or send the simulation beacon frames to the first terminal ata gradually decreasing transmit power, so that the first terminaldetermines that the first AP is sending a beacon frame. When a beaconframe signal detected by the first terminal is weak, the first terminalmay determine that weakening of the beacon frame signal from the firstAP indicates quality degradation of communication between the firstterminal and the first AP. Therefore, the first terminal may initiateroaming, that is, proactive roaming of the first terminal is triggered.Different terminals may have different configurations. After channelswitching, if a terminal receives no beacon frame, roaming of theterminal is not triggered and the terminal may return to a channel usedbefore the switching. Therefore, sending a beacon frame by the second APby simulating the first AP can improve compatibility between theterminal and the AP. In addition, in another optional manner oftriggering terminal roaming, the second AP does not send a simulationbeacon frame after the first terminal switches to the operating channelof the second AP.

Optionally, the second AP periodically sends multiple simulation beaconframes to the first terminal by using the second channel. The multiplesimulation beacon frames include the simulation beacon frame sent at thefirst power. After a quantity of times that the second AP sends thesimulation beacon frames reaches a threshold, the second AP stopssending the simulation beacon frames.

The threshold herein may be specified according to an actual condition,for example, the threshold may be three or four simulation beaconframes. The second AP stops sending the simulation beacon frames to thefirst terminal. If the terminal receives no beacon frame within a presettime period, roaming is triggered.

It can be known that the second AP triggers proactive roaming of thefirst terminal by sending, to the first terminal, a simulation beaconframe whose signal strength is weak, or triggers proactive roaming ofthe first terminal by not sending a simulation beacon frame.

In another embodiment, if the first AP selects, by using a preset secondalgorithm, the second AP as an AP with which the first terminal needs tofinally associate, that is, a target AP, the first AP determines whetheran AP associated with the first terminal after the first terminalproactively roams is the second AP. If no, the steps in the foregoingembodiment are repeated. That is, when the first terminal roams to anon-target AP, that is, a transitive AP, the transitive AP triggersproactive roaming of the first terminal, and the transitive AP adds theMAC address of the first terminal to a temporary blacklist, to preventthe first terminal from roaming to the transitive AP again, until thefirst terminal roams to the second AP. When the first terminal roams tothe second AP, the transitive AP obtains, by means of a switch, acontroller, or communication between APs, a message indicating that thefirst terminal has associated with the target AP. At this moment, thetransitive AP removes the MAC address of the first terminal from thetemporary blacklist.

With reference to FIG. 1, in a process of switching from the AP 1 to theAP 2 by the terminal, the AP 1 may be referred to as the first AP, andthe AP 1 triggers channel switching of the terminal; the AP 2 may bereferred to as the second AP, and optionally, the AP 2 sends asimulation beacon frame and/or a data frame to the terminal. In aprocess of switching from the AP 2 to the AP 1 by another terminal, thesecond AP triggers channel switching of the another terminal, andoptionally, the first AP sends a simulation beacon frame and/or a dataframe to the terminal.

FIG. 3 is a possible schematic structural diagram of an access pointinvolved in the foregoing embodiment.

The access point includes at least a sending unit 310, configured tosend, by using a first channel, a unicast channel switching message to afirst terminal associated with the AP. The unicast channel switchingmessage is used to instruct the first terminal to switch from the firstchannel to a second channel. A receiver address of the unicast channelswitching message is an address of the first terminal. The first channelis an operating channel of the AP. The second channel and the firstchannel are different.

After the unicast channel switching message is sent, the first channelis retained as the operating channel of the AP.

Optionally, the access point may further include: a receiving unit 320,configured to receive an instruction message sent by a second AP, wherethe instruction message instructs a second terminal associated with thesecond AP to switch to the first channel, the instruction messageincludes a BSSID of the second AP and an address of the second terminal,and an operating channel of the second AP and the first channel aredifferent; and a transmission unit 330, configured to transmit a dataframe to the second terminal according to the address of the secondterminal, where a BSSID field of the data frame is filled in with theBSSID of the second AP.

Optionally, the receiving unit 320 is further configured to receive aninstruction message sent by a second AP, where the instruction messageinstructs a second terminal associated with the second AP to switch tothe first channel, the instruction message includes a BSSID of thesecond AP and an address of the second terminal, and an operatingchannel of the second AP and the first channel are different; thesending unit 310 is further configured to send a simulation beacon frameto the second terminal at a first power by using the first channel,where a first address field of the simulation beacon frame includes theaddress of the second terminal, a second address field of the simulationbeacon frame includes the BSSID of the second AP, and a third addressfield of the simulation beacon frame includes the BSSID of the secondAP. The first power is less than a default transmit power of the firstAP.

Optionally, the receiving unit 320 is further configured to receive aninstruction message sent by a second AP, where the instruction messageincludes a BSSID of the second AP, the instruction message instructs theAP to send a simulation beacon frame by using the BSSID of the secondAP, and an operating channel of the second AP and the first channel aredifferent; the sending unit 310 is further configured to send asimulation beacon frame at a first power by using the first channel,where a first address field of the simulation beacon frame includes abroadcast address.

Optionally, the access point further includes a stopping unit 340.

The sending unit 310 is further configured to periodically send multiplesimulation beacon frames to the second terminal by using the firstchannel. The multiple simulation beacon frames include the simulationbeacon frame sent at the first power.

The stopping unit 340 is configured to: after a quantity of times thatthe AP sends the simulation beacon frames reaches a threshold, stopsending the simulation beacon frames.

Functions of functional modules of the access point can be implementedby means of the steps in the foregoing embodiment. Therefore, a specificworking process of the access point provided in the present invention isnot described herein again.

FIG. 4 is another possible schematic structural diagram of an accesspoint involved in the foregoing embodiment.

The access point includes at least a transceiver 410 (for example, anantenna) and a processing circuit 420, and optionally, may furtherinclude a memory 430. The processing circuit 420 may include a processor421, a radio frequency circuit 422, and a baseband 423.

The processor 421 may be a central processing unit (CPU) or acombination of a CPU and a hardware chip. The hardware chip may be anapplication-specific integrated circuit (ASIC), a programmable logicdevice (PLD), or a combination thereof. The PLD may be a complexprogrammable logic device (CPLD), a field-programmable gate array(FPGA), a generic array logic (GAL), or any combination thereof.

The memory 430 may include a volatile memory, for example, arandom-access memory (RAM). The memory 430 may also include anon-volatile memory, for example, a read-only memory (ROM), a flashmemory, a hard disk drive (HDD), or a solid-state drive (SSD). Thememory 430 may further include a combination of the foregoing memories.The memory 430 stores program code, and transmits the stored programcode to the processor 421.

The transceiver 410 is configured to send, by using a first channel, aunicast channel switching message to a first terminal associated withthe AP. The unicast channel switching message is used to instruct thefirst terminal to switch from the first channel to a second channel. Areceiver address of the unicast channel switching message is an addressof the first terminal. The first channel is an operating channel of theAP. The second channel and the first channel are different.

The processing circuit 420 is configured to retain the first channel asthe operating channel of the AP after the unicast channel switchingmessage is sent.

The processor 421 executes various functions used for communication withthe first terminal. On an uplink, the transceiver 410 receives an uplinksignal from the first terminal, and performs demodulation on the uplinksignal. Then, the processor 421 performs processing to restore servicedata and signaling information sent by the first terminal. On adownlink, the processor 421 performs processing on service data andsignaling information, and the transceiver 410 performs demodulation togenerate a downlink signal and transmits the downlink signal to thefirst terminal. The processor 421 also executes a processing processrelated to an access point in FIG. 2 and/or another process used for atechnology described in this application. The memory 430 is configuredto store program code and data of the access point.

Steps of methods or algorithms described in the embodiments disclosed inthis specification may be implemented by hardware, a software moduleexecuted by a processor, or a combination thereof. A softwareinstruction may include a corresponding software module. The softwaremodule may be stored in a random access memory, a flash memory, aread-only memory, an erasable programmable read-only memory (EPROM), anelectrically erasable programmable read-only memory (EEPROM), a harddisk, a compact disc read-only memory (CD-ROM), or any other form ofstorage medium well known in the art. An exemplary storage medium iscoupled with the processor, so that the processor can read informationfrom the storage medium and write information into the storage medium.Certainly, the storage medium may also be a component of the processor.The processor and the storage medium may be located in an ASIC. Inaddition, the ASIC may be located in user equipment. Certainly, theprocessor and the storage medium may be located in the user equipment asdiscrete components.

A person of skill in the art should be able to realize that in one ormore of the foregoing examples, the functions described in the presentinvention may be implemented by using hardware, software, firmware, orany combination thereof. When the present invention is implemented byusing software, the foregoing functions may be stored in acomputer-readable medium or transmitted as one or more instructions orcode in the computer-readable medium.

The objectives, technical solutions, and benefits of the presentinvention are further described in detail in the foregoing specificembodiments. It should be understood that the foregoing descriptions areonly specific embodiments of the present invention, but are not intendedto limit the protection scope of the present invention. Anymodification, equivalent replacement, or improvement made based on thesolution of the present invention shall fall within the protection scopeof the present invention.

What is claimed is:
 1. A method for triggering terminal roaming by anaccess point (AP), the method comprising: sending, by a first AP over afirst channel, a unicast channel switching message to a first terminalassociated with the first AP, wherein the unicast channel switchingmessage instructs the first terminal to switch from the first channel toa second channel, a receiver address of the unicast channel switchingmessage is an address of the first terminal, the first channel is anoperating channel of the first AP, and the second channel and the firstchannel are different; and retaining the first channel as the operatingchannel of the first AP after the unicast channel switching message issent.
 2. The method according to claim 1, further comprising: receiving,by the first AP, an instruction message sent by a second AP, wherein theinstruction message instructs a second terminal associated with thesecond AP to switch to the first channel, the instruction messagecomprises a basic service set identifier (BSSID) of the second AP and anaddress of the second terminal, and an operating channel of the secondAP and the first channel are different; and transmitting, by the firstAP, a data frame to the second terminal according to the address of thesecond terminal, wherein a BSSID field of the data frame is filled inwith the BSSID of the second AP.
 3. The method according to claim 1,further comprising: receiving, by the first AP, an instruction messagesent by a second AP, wherein the instruction message instructs a secondterminal associated with the second AP to switch to the first channel,the instruction message comprises a basic service set identifier (BSSID)of the second AP and an address of the second terminal, and an operatingchannel of the second AP and the first channel are different; andsending, by the first AP, a simulation beacon frame to the secondterminal at a first power by using the first channel, wherein a firstaddress field of the simulation beacon frame comprises the address ofthe second terminal, a second address field of the simulation beaconframe comprises the BSSID of the second AP, and a third address field ofthe simulation beacon frame comprises the BSSID of the second AP, andthe first power is less than a default transmit power of the first AP.4. The method according to claim 1, further comprising: receiving, bythe first AP, an instruction message sent by a second AP, wherein theinstruction message comprises a basic service set identifier (BSSID) ofthe second AP, the instruction message instructs the first AP to send asimulation beacon frame by using the BSSID of the second AP, and anoperating channel of the second AP and the first channel are different;and sending, by the first AP, the simulation beacon frame at a firstpower by using the first channel, wherein a first address field of thesimulation beacon frame comprises a broadcast address, and the firstpower is less than a default transmit power of the first AP.
 5. Themethod according to claim 4, further comprising: periodically sending,by the first AP, multiple simulation beacon frames to the secondterminal by using the first channel, wherein the multiple simulationbeacon frames comprise the simulation beacon frame sent at the firstpower; and after a quantity of times that the first AP sends thesimulation beacon frames reaches a threshold, stopping, by the first AP,sending the simulation beacon frames.
 6. An access point (AP)comprising: a processor; and a memory storing instructions that whenexecuted configure the processor to: send, over a first channel, aunicast channel switching message to a first terminal associated withthe AP, wherein the unicast channel switching message instructs thefirst terminal to switch from the first channel to a second channel, areceiver address of the unicast channel switching message is an addressof the first terminal, the first channel is an operating channel of theAP, and the second channel and the first channel are different; andretain the first channel as the operating channel of the AP after theunicast channel switching message is sent.
 7. The AP according to claim6, wherein the memory further stores instructions that when executedconfigure the processor to: receive an instruction message sent by asecond AP, wherein the instruction message instructs a second terminalassociated with the second AP to switch to the first channel, theinstruction message comprises a basic service set identifier (BSSID) ofthe second AP and an address of the second terminal, and an operatingchannel of the second AP and the first channel are different; andtransmit a data frame to the second terminal according to the address ofthe second terminal, wherein a BSSID field of the data frame is filledin with the BSSID of the second AP.
 8. The AP according to claim 6,wherein the memory further stores instructions that when executedconfigure the processor to: receive an instruction message sent by asecond AP, wherein the instruction message instructs a second terminalassociated with the second AP to switch to the first channel, theinstruction message comprises a basic service set identifier (BSSID) ofthe second AP and an address of the second terminal, and an operatingchannel of the second AP and the first channel are different; and send asimulation beacon frame to the second terminal at a first power by usingthe first channel, wherein a first address field of the simulationbeacon frame comprises the address of the second terminal, a secondaddress field of the simulation beacon frame comprises the BSSID of thesecond AP, and a third address field of the simulation beacon framecomprises the BSSID of the second AP; and the first power is less than adefault transmit power of the first AP.
 9. The AP according to claim 6,wherein the memory further stores instructions that when executedconfigure the processor to: receive an instruction message sent by asecond AP, wherein the instruction message comprises a basic service setidentifier (BSSID) of the second AP, the instruction message instructsthe AP to send a simulation beacon frame by using the BSSID of thesecond AP, and an operating channel of the second AP and the firstchannel are different; and send the simulation beacon frame at a firstpower by using the first channel, wherein a first address field of thesimulation beacon frame comprises a broadcast address, and the firstpower is less than a default transmit power of the first AP.
 10. The APaccording to claim 9, wherein the memory further stores instructionsthat when executed configure the processor to: periodically sendmultiple simulation beacon frames to the second terminal by using thefirst channel, wherein the multiple simulation beacon frames comprisethe simulation beacon frame sent at the first power; and after aquantity of times that the AP sends the simulation beacon frames reachesa threshold, stop sending the simulation beacon frames.
 11. An accesspoint (AP) comprising a transceiver and a processing circuit, wherein:the processing circuit is configured to send, by using the transceiverand a first channel, a unicast channel switching message to a firstterminal associated with the AP, wherein the unicast channel switchingmessage instructs the first terminal to switch from the first channel toa second channel, a receiver address of the unicast channel switchingmessage is an address of the first terminal, the first channel is anoperating channel of the AP, and the second channel and the firstchannel are different; and the processing circuit is further configuredto retain the first channel as the operating channel of the AP after theunicast channel switching message is sent.
 12. The AP according to claim11, wherein: the processing circuit is further configured to receive aninstruction message sent by a second AP, wherein the instruction messageinstructs a second terminal associated with the second AP to switch tothe first channel, the instruction message comprises a basic service setidentifier (BSSID) of the second AP and an address of the secondterminal, and an operating channel of the second AP and the firstchannel are different; and transmit a data frame to the second terminalaccording to the address of the second terminal, wherein a BSSID fieldof the data frame is filled in with the BSSID of the second AP.
 13. TheAP according to claim 11, wherein: the processing circuit is furtherconfigured to: receive an instruction message sent by a second AP,wherein the instruction message instructs a second terminal associatedwith the second AP to switch to the first channel, the instructionmessage comprises a basic service set identifier (BSSID) of the secondAP and an address of the second terminal, and an operating channel ofthe second AP and the first channel are different; and send a simulationbeacon frame to the second terminal at a first power by using the firstchannel, wherein a first address field of the simulation beacon framecomprises the address of the second terminal, a second address field ofthe simulation beacon frame comprises the BSSID of the second AP, and athird address field of the simulation beacon frame comprises the BSSIDof the second AP; and the first power is less than a default transmitpower of the first AP.
 14. The AP according to claim 11, wherein: theprocessing circuit is further configured to: receive an instructionmessage sent by a second AP, wherein the instruction message comprises abasic service set identifier (BSSID) of the second AP, the instructionmessage instructs the AP to send a simulation beacon frame by using theBSSID of the second AP, and an operating channel of the second AP andthe first channel are different; and send the simulation beacon frame ata first power by using the first channel, wherein a first address fieldof the simulation beacon frame comprises a broadcast address, and thefirst power is less than a default transmit power of the first AP. 15.The AP according to claim 14, wherein: the processing circuit is furtherconfigured to periodically send multiple simulation beacon frames to thesecond terminal by using the first channel, wherein the multiplesimulation beacon frames comprise the simulation beacon frame sent atthe first power; and the processing circuit is configured to: after aquantity of times that the AP sends the simulation beacon frames reachesa threshold, stop sending the simulation beacon frames.